The use of light-emitting diodes (LEDs) in lighting is becoming increasingly common, in particular because it is possible to create arrays of diodes that are capable of providing a powerful light with a high efficiency. LED lighting devices are therefore finding an increasing number of applications, such as in the automotive sector, for producing parking lights and headlights, or indeed in the production of lighting for passenger compartments, such as status lights or comfort lights.
Nonetheless, incandescent lamp lighting devices still play an important role, in particular in the automotive sector.
As a result, in particular in the automotive sector, incandescent lamps and LED lights sometimes have to be supplied with power by one and the same power supply device.
Now, these two kinds of structures have different and sometimes incompatible restrictions.
FIG. 1A shows one common solution for supplying power to an incandescent lamp, in which a power supply module PLT1 makes it possible to couple the lamp LMP to a supply voltage source Vbat (this kind of power supply module, connected between a supply voltage and the load, is commonly referred to as a high-side driver).
However, incandescent lamps draw high inrush currents at the instant when they are activated, whereas power consumption is relatively modest during normal operation.
FIG. 1B shows the current, upon switching on an incandescent lamp, that a power supply module, for example a high-side driver, needs to provide in order to supply such an incandescent lamp with power. On account of an impedance that varies with temperature, the inrush current Ipk upon switching on the lamp is around ten times greater than the stabilized current Istab during normal operation.
As a result, the power supply module PLT1 must be capable of providing a current at least equal to the inrush current Ipk without being damaged. This is highly constrictive as to the technology used and in terms of the size of the components. Specifically, the power supply module PLT1 customarily includes a power transistor that has to be dimensioned to transmit a very high current, and that is consequently large in size.
One solution making it possible to reduce the size of the components of the power supply module PLT1 consists in supplying power to the incandescent lamp using a pulse width modulation (PWM) technique. In the PWM technique, the current is transmitted by peaks of short duration, making it possible to provide the power necessary for the on/off switch-on phase without impairing a power supply module PLT1, the power transistor of which, for example, is however dimensioned to provide a lower current, of the order of the stabilized current Istab.
Moreover, LED lighting devices, such as three-color lights LEDRGB (shown for example in FIG. 2B), are typically produced on a printed circuit board MLED, allowing the lighting to be managed. This kind of printed circuit board includes, for example, a bus interface INT, a local microcontroller CMDL and a three-color light-emitting diode LEDRGB.
Such LED lighting devices or ‘LED blocks’ MLED generally have a residual current consumption when switched off, stemming for example from the consumption of the microcontroller CMDL in standby mode. This is detrimental in particular for devices that are battery-operated, such as in automotive equipment.
FIG. 2A shows one common solution making it possible to reduce electricity consumption when the block MLED is not being used. When switched off, the power supply Vbat is disconnected from the printed circuit board MLED by virtue of an external on/off switch SWext commanded by a power supply module PLT2.
However, upon closure of the on/off switch SWext, a current peak is imposed by a decoupling capacitor Cdec as the latter is charged to the supply voltage Vbat.
As a result, the on/off switch SWext must also be dimensioned so as to deliver such an inrush current, which is far higher than the operating current in the stable regime. This also leads to an excessive bulk, on the one hand through the size of the on/off switch and on the other hand through the ‘external’ aspect of the component, outside of an integrated circuit.
PWM techniques are not compatible with this kind of printed circuit board, as the logic circuits of the microcontrollers CMDL and of the bus interface INT receive said PWM pulses as a multitude of reset signals and can cause the system to block.
As a result, a power supply device capable of supplying power both to an incandescent lamp LMP and to a block MLED currently has to be dimensioned to allow the higher inrush current of those drawn by the two kinds of lighting device structure to flow, or include a PWM power supply device that is also able to command an external on/off switch that is dimensioned to allow the inrush current drawn by a block MLED to flow.
In both cases, the bulk of the power supply device is non-negligible. It would therefore be desirable to produce an integrated power supply device (that is to say without any external component) that has little bulk, for example by being dimensioned to allow a low stable regime current to flow.